A conventional chain saw has an internal combustion engine such as an air cooled two-cycle gasoline engine as a power source. The inventors'previously proposed air inlet apparatus for an internal combustion engine of this type having the construction (Japanese Patent Application Laid Open No. 195891/-1993) where an air inlet port is provided on the upper part of the main body of the machine, and an air path is provided inside the main body so as to allow the air flowing from the air inlet port to flow onto the upper part of the engine and then downwardly using the intake manifold pressure generated by a cooling fan chamber of the engine. A filter is provided in the air path so that the surface of the filter through which air supplied to the carburetor chamber passes faces to the inner wall of the air path. The air flow into the carburetor chamber intersects the surface of the filter.
According to this air inlet apparatus, any dust contained in the air is removed by the filter and the dust accumulated on the surface of the filter are blown down along the surface of the filter by the air passing in the air path from the top downwardly. Therefore, clogging of the filter is avoided and high filtration performance of the filter can be maintained.
However, as the air inlet port is provided on the upper part of the main body of the chain saw, there were cases where the air inlet port was covered by snow during outdoor work in the winter and the filter frozen inside the main body by water invading the engine from the air inlet port. During operation in the rain during the summer, water also interfered with the filter function, as water invaded the air inlet port resulting in failure of the internal combustion engine.